A conventional image-reader known in the art is provided with a first image-reading unit and a second image-reading unit disposed on a path along which a document sheet is conveyed. The first image-reading unit is provided for one surface of the document sheet, and the second image-reading unit for the other surface of the document sheet, whereby the first and second image-reading unit can simultaneously read both surfaces of a document sheet conveyed along the conveying path.
Japanese Patent Application Publication No. 2002-359721 proposes an image-reader that has a first image-reading unit and a second image-reading unit and controls the first image-reading unit based on the cycle count of a clock signal inputted into the first image-reading unit and controls the second image-reading unit based on the cycle count of a clock signal inputted into the second image-reading unit. The proposed image-reader also attempts to decrease the difference in read times between the first and second image-reading units by comparing each of their clock cycle counts with predetermined reference values.